It is proposed to subject up to 3,000 families to a 3-hour testing session in which a battery of 15 psychometric tests, measuring various cognitive abilities, and an environmental questionnaire are completed by father, mother, and at least one child over 14 years of age, a blood and saliva sample is taken for blood groups and genetic markers studies. So far 2,366 families have been tested. The objectives of the study are (1) to estimate the heritabilities and genetic correlations of scores on the selected cognitive tests, (2) to compare phenotypic and genetic cognitive factor structure, (3) to measure the effects of inbreeding, assortative mating, ancestry, parental age, birth order, certain maternal-fetal risks, and socio-economic variables, (4) to search for possible relationships between cognitive traits and genetic markers, and between cognitive and dermatoglyphic traits, and (5) to search for non-additive genetic effects (heterosis, dominance, epistasis) in components of the cognitive abilities tested. BIBLIOGRAPHIC REFERENCES: Johnson, R.C., DeFries, J.C., Wilson, J.R., McClearn, G.E., Vandenberg, S.G., Ashton, G.C., Mi, M.P., and Rashad, M.N. Assortative Marriage for Specific Cognitive Abilities in Two Ethnic Groups. Human Biology, May 1976, Vol. 48, No. 2, pp 343-352. Ashton G.C. and Polovina, J. Path Analysis of Familial Relationships of Fifteen Tests of Cognitive Ability and Four Derived Factor Scores. Presented at the Behavior Genetics Association meeting, Boulder, Colorado, June 17-19, 1976.